1. Field of the Invention
The present invention relates to an activating device in a passenger protection apparatus to cause to activate a passenger protection apparatus such as for example an airbag apparatus during a vehicle collision.
2. Related Art
A device as indicated in FIG. 3 has been already devised as an activating device to cause to activate a passenger protection apparatus such as, for example, an airbag apparatus, when a vehicle collision has been occurred.
As shown in FIG. 3, the activating device is structured by means of a sensor 1a for the purpose of detecting the vehicle collision, an ignition drive transistor 2a, an activating element 3a, a multivibrator 4a, and a transistor 5a for applying an activating current to the activating element 3a.
When attempting to detect a side-collision of the vehicle with the sensor 1a, the sensor 1a is disposed in a door portion or the like which is the side portion of the vehicle. Contacts of the sensor 1a close in correspondence to acceleration or load generated during the side-collision of the vehicle. When the contacts of the sensor 1a are closed, the sensor 1a supplies the activating current from a power source (not illustrated) to the activating element 3a. However, in case the sensor 1a is disposed in a door portion for the purpose of detecting the side-collision of the vehicle, the sensor 1a must be installed in a narrow space of a door inner portion of the vehicle. Additionally, supply of the activating current for a specified time is required for the purpose of causing to activate the passenger protection apparatus such as the airbag apparatus. This is because the possibility exists that the passenger protection apparatus may not be activated accurately if the supply of the activating current is not maintained for the specified time. It is necessary to maintain the supply of the activating current for the specified time.
However, a sensor of mechanical type composed of a moving body and spring or the like cannot be employed as the sensor 1a required to be installed in the narrow space such as the door inner portion where is no margin in installation space. This is because the sensor of mechanical type is difficult to form in a compact configuration due to the structure thereof. Additionally, since the sensor of mechanical type must maintain an "on" state and continue to supply the activating current for the specified time, measures must inevitably be taken. An example of the measures is to lengthen the stroke of the moving body of the mechanical type sensor. However, the "on" state for the specified time is assured by means of this measure, while the configuration of the mechanical type sensor inevitably becomes large, and the installation in the narrow space such as the door inner portion of the vehicle is impossible. Moreover, in a case whereby the sensor of mechanical type is installed in the door inner portion, the moving body or spring may operate and the side-collision of the vehicle may be erroneously detected in response to shock when the door of the vehicle is closed.
For these reasons, as the sensor 1a for side-collision detection use, a collision detection sensor of contact type (hereinafter termed a "touch sensor") is employed. The touch sensor, which is disclosed in for example Japanese Patent Publication No. Hei 5-45371 (equivalent to U.S. Pat. No. 5,307,896), can be formed compactly and moreover does not erroneously detect the shock caused by closing the door of the vehicle. The touch sensor can be formed compactly as described above, but because a conductive body makes contact and goes "on" state based on a deformation of the door portion due to the side-collision, it cannot maintain the "on" state, i.e., the supply of the activating current for the specified time. Maintaining the supply of the activating current for the specified time is necessary to accurately cause to activate the passenger protection apparatus. Accordingly, the multivibrator 4a is employed to maintain the supply of the activating current for the specified time.
That is to say, in a case whereby the contacts of the sensor 1a closes in correspondence to the deformation of the door portion of the vehicle, the closure of the contacts is detected by means of the multivibrator 4a. When the multivibrator 4a detects the closure of the contacts, the multivibrator 4a outputs a pulse signal with a predetermined pulse width to a base of the transistor 5a connected to the sensor 1a. The transistor 5a is turned on with the pulse signal and is maintained the "on" state so as to supply the activating current to the activating element 3a for the specified time.
Additionally, in a case whereby the side-collision of the vehicle has been detected by means of an acceleration sensor (not illustrated) installed in an electrical control unit (ECU) 12, the ignition drive transistor 2a receives a driving signal from a central processing unit (CPU) based on a detection signal from the acceleration sensor and supplies the activating current to the activating element 3a.
However, according to the prior art, as is shown in FIG. 3, the multivibrator 4a and the ECU 12 including the CPU are employed in order to maintain the supply of the activating current to the activating element 3a and to activate the activating element 3a. In maintaining the supply of the activating current described above, a strong possibility exists of receiving large adverse effects due to electromagnetic buffering and electrical obstruction. That is to say, in a case where the adverse effects are received, even in a case wherein the sensor la has not detected the vehicle collision, there may be cases wherein the multivibrator 4a makes the transistor 5a conductable. Similarly, the possibility exists that the central processing unit (CPU) may make the ignition drive transistor 2a conductable. In cases such as these, the activating element 3a is erroneously activated and the passenger protection apparatus operates erroneously, and so this becomes a cause which reduces the reliability of the passenger protection apparatus.